31x10.50 R15 vs 285/65 R18

What changes when you change tire size?

285/65 R18 is outside the configured tolerance for 31x10.50 R15: +5.1% diameter and +5.1% speedometer effect.

Geometric comparison

Geometric comparison
Metric This size: 31x10.50 R15 Alternative: 285/65 R18 Difference Verdict
Overall diameter 31.00 in 32.59 in +5.1% Too tall
Section width 10.50 in 11.22 in +0.72 in Computed difference
Sidewall height 8.00 in 7.29 in -0.71 in Computed difference
Circumference 97.39 in 102.37 in +5.1% Too tall
Speedo 0.0% +5.1% +5.1% Outside tolerance

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Looks valid
Looks valid
Units
Editorial preset

These are TireFitLab editorial diameter-screening presets. Regional names choose a preset, not a national legal limit, ETRTO rule or vehicle approval. The AWD preset does not establish an allowable drivetrain mismatch. Use the exact vehicle and tyre manufacturer instructions; nominal geometry alone cannot approve fitment.

High fitment riskOut of tolerance · Diameter +5.1% (+1.59 in) · US preset (±3%)
  • High fitment risk · This rating covers tire geometry only, not vehicle compatibility.
  • Diameter +5.1% · Ride-height change +0.79 in.
  • Speedometer reads low · 60 mph → 63.1 mph.
  • Sidewall -0.71 in · Width +0.72 in.
Diameter+5.1%+1.59 in
Speedo @ 60+5.1%60 mph → 63.1 mph
Sidewall-0.71 inWidth +0.72 in
Ride-height change+0.79 inDiameter ÷ 2
How this result is calculated

Computed from nominal tire-size geometry: diameter, circumference and speedometer error. It does not check vehicle placard approval, load/speed rating, rim-width range, wheel-arch, suspension or brake clearance.

Methodology

Before fitting

  • Check the vehicle placard and owner’s manual first.
  • Match or exceed the required load index and speed rating.
  • Confirm rim-width range, bolt pattern, hub bore, offset and fasteners.
  • Inspect wheel-arch, suspension and brake clearance under real vehicle load.
  • Check TPMS, cold pressure and local roadworthiness rules.
Diameter
31.00 in 32.59 in+1.59 in
Sidewall
8.00 in 7.29 in-0.71 in
Width
10.50 in 11.22 in+0.72 in
Circumference
97.39 in 102.37 in+5.1%
Revs / mile
651 619
Speedo @ 60
60 mph 63.1 mph+5.1%
Ride-height change
0.00 in +0.79 in
True distance per 100 indicated
100 mi 105.1 mi+5.1%
Δ⌀ +1.59 inΔ↔ +0.72 in
  • Current — 31x10.50 R15
  • New — 285/65 R18
  • Grounded to the road: the axle rises +0.79 in.

Tires and wheels in one comparison

Result report

31x10.50 R15 285/65 R18 · High fitment risk · Out of tolerance

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Geometric estimate. Always verify physical clearance (arches, suspension, brakes) before fitting.

In-tolerance alternative sizes

In-tolerance alternative sizes
SizeDiameterSpeedo @ 100Use this
−1″ 265/80R14-1.0%-1.0%
OE 265/75R15-1.1%-1.1%
+1″ 275/70R16+0.5%+0.5%
+2″ 265/70R17+2.0%+2.0%

31x10.50 R15 · 285/65 R18 · Methodology